HID: apple: Add support for magic keyboard backlight on T2 Macs

Unlike T2 Macs with Butterfly keyboard, who have their keyboard backlight
on the USB device the T2 Macs with Magic keyboard have their backlight on
the Touchbar backlight device (05ac:8102).

Support for Butterfly keyboards has already been added in
commit 9018eacbe623 ("HID: apple: Add support for keyboard backlight on
certain T2 Macs.") This patch adds support for the Magic keyboards.

Signed-off-by: Orlando Chamberlain <[e-mail]>
Co-developed-by: Aditya Garg <[e-mail]>
Signed-off-by: Aditya Garg <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Benjamin Tissoires <[e-mail]>

drivers/hid/hid-apple.c

···
  *  Copyright (c) 2006-2007 Jiri Kosina
  *  Copyright (c) 2008 Jiri Slaby <[e-mail]>
  *  Copyright (c) 2019 Paul Pawlowski <[e-mail]>
+ *  Copyright (c) 2023 Orlando Chamberlain <[e-mail]>
+ *  Copyright (c) 2024 Aditya Garg <[e-mail]>
  */
 
 /*
···
 #include <linux/timer.h>
 #include <linux/string.h>
 #include <linux/leds.h>
+#include <dt-bindings/leds/common.h>
 
 #include "hid-ids.h"
 
···
 #define APPLE_RDESC_BATTERY	BIT(9)
 #define APPLE_BACKLIGHT_CTL	BIT(10)
 #define APPLE_IS_NON_APPLE	BIT(11)
+#define APPLE_MAGIC_BACKLIGHT	BIT(12)
 
 #define APPLE_FLAG_FKEY		0x01
 
 #define HID_COUNTRY_INTERNATIONAL_ISO	13
 #define APPLE_BATTERY_TIMEOUT_MS	60000
+
+#define HID_USAGE_MAGIC_BL			0xff00000f
+#define APPLE_MAGIC_REPORT_ID_POWER		3
+#define APPLE_MAGIC_REPORT_ID_BRIGHTNESS	1
 
 static unsigned int fnmode = 3;
 module_param(fnmode, uint, 0644);
···
 struct apple_sc_backlight {
 	struct led_classdev cdev;
 	struct hid_device *hdev;
+};
+
+struct apple_magic_backlight {
+	struct led_classdev cdev;
+	struct hid_report *brightness;
+	struct hid_report *power;
 };
 
 struct apple_sc {
···
 	return ret;
 }
 
+static void apple_magic_backlight_report_set(struct hid_report *rep, s32 value, u8 rate)
+{
+	rep->field[0]->value[0] = value;
+	rep->field[1]->value[0] = 0x5e; /* Mimic Windows */
+	rep->field[1]->value[0] |= rate << 8;
+
+	hid_hw_request(rep->device, rep, HID_REQ_SET_REPORT);
+}
+
+static void apple_magic_backlight_set(struct apple_magic_backlight *backlight,
+				     int brightness, char rate)
+{
+	apple_magic_backlight_report_set(backlight->power, brightness ? 1 : 0, rate);
+	if (brightness)
+		apple_magic_backlight_report_set(backlight->brightness, brightness, rate);
+}
+
+static int apple_magic_backlight_led_set(struct led_classdev *led_cdev,
+					 enum led_brightness brightness)
+{
+	struct apple_magic_backlight *backlight = container_of(led_cdev,
+			struct apple_magic_backlight, cdev);
+
+	apple_magic_backlight_set(backlight, brightness, 1);
+	return 0;
+}
+
+static int apple_magic_backlight_init(struct hid_device *hdev)
+{
+	struct apple_magic_backlight *backlight;
+	struct hid_report_enum *report_enum;
+
+	/*
+	 * Ensure this usb endpoint is for the keyboard backlight, not touchbar
+	 * backlight.
+	 */
+	if (hdev->collection[0].usage != HID_USAGE_MAGIC_BL)
+		return -ENODEV;
+
+	backlight = devm_kzalloc(&hdev->dev, sizeof(*backlight), GFP_KERNEL);
+	if (!backlight)
+		return -ENOMEM;
+
+	report_enum = &hdev->report_enum[HID_FEATURE_REPORT];
+	backlight->brightness = report_enum->report_id_hash[APPLE_MAGIC_REPORT_ID_BRIGHTNESS];
+	backlight->power = report_enum->report_id_hash[APPLE_MAGIC_REPORT_ID_POWER];
+
+	if (!backlight->brightness || !backlight->power)
+		return -ENODEV;
+
+	backlight->cdev.name = ":white:" LED_FUNCTION_KBD_BACKLIGHT;
+	backlight->cdev.max_brightness = backlight->brightness->field[0]->logical_maximum;
+	backlight->cdev.brightness_set_blocking = apple_magic_backlight_led_set;
+
+	apple_magic_backlight_set(backlight, 0, 0);
+
+	return devm_led_classdev_register(&hdev->dev, &backlight->cdev);
+
+}
+
 static int apple_probe(struct hid_device *hdev,
 		const struct hid_device_id *id)
 {
···
 	if (quirks & APPLE_BACKLIGHT_CTL)
 		apple_backlight_init(hdev);
 
+	if (quirks & APPLE_MAGIC_BACKLIGHT) {
+		ret = apple_magic_backlight_init(hdev);
+		if (ret)
+			goto out_err;
+	}
+
 	return 0;
+
+out_err:
+	del_timer_sync(&asc->battery_timer);
+	hid_hw_stop(hdev);
+	return ret;
 }
 
 static void apple_remove(struct hid_device *hdev)
···
 		.driver_data = APPLE_HAS_FN | APPLE_ISO_TILDE_QUIRK | APPLE_RDESC_BATTERY },
 	{ HID_BLUETOOTH_DEVICE(BT_VENDOR_ID_APPLE, USB_DEVICE_ID_APPLE_MAGIC_KEYBOARD_NUMPAD_2021),
 		.driver_data = APPLE_HAS_FN | APPLE_ISO_TILDE_QUIRK },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_APPLE, USB_DEVICE_ID_APPLE_TOUCHBAR_BACKLIGHT),
+		.driver_data = APPLE_MAGIC_BACKLIGHT },
 
 	{ }
 };